The present invention, in some embodiments thereof, relates to Computer Generated Holograms (CGHs) and, more particularly, but not exclusively, to methods and apparatus for increasing an observing window through which a CGH can be viewed.
CGHs may be produced by projecting coherent light onto computer controlled Spatial Light Modulators (SLMs). The SLMs include an array of light modulators which are programmed by a computer to modulate light, so that light coming off the SLM (passing through or reflected off the SLM) produces a hologram.
The term SLM is used herein to describe a device which produces holograms. In some embodiments, the device is an SLM which modulates light which illuminates the SLM, acting by reflection or by transmission, however, the term is also meant to include an array which both produces light and modulates the light in order to produce a CGH.
An observation window of a CGH is limited in size. An observation window of a CGH is typically small, approximately a size of a person's pupil.
The small size limits the angles from which a viewer can view an image of the CGH.
In some implementations of CGH-producing systems, such as, for example, an implementation described in PCT published patent application WO 2010/004563 by Rotschild et al, a viewer tracking system is used to direct the observation window to a viewer's eyes. For a small size observing window, viewing is not easy in case of a stationary position, and in case of a moving viewer accuracy and cost of a viewer tracking system can affect usability and cost of the CGH-producing systems.
An ability to increase a size of an observing window can have a large impact on the field of 3D holographic devices, both for stationary viewing positions and for dynamic/tracking related viewing positions.
Background art includes:
K. Maeno, N. Fukaya, O. Nishikawa, “Electro holographic display using 15 Mega pixels LCD”, Advanced 3D Telecommunication Project 1996, SPIE Vol. 2652;
T. Mishina, M. Okui, F. Okano, “Viewing zone enlargement method for sampled hologram that uses high order diffraction”, Applied Optics 2002, Vol. 41, No. 8;
PCT Published Patent Application WO 2010/004563;
U.S. Published Patent Application 2006/0172008;
PCT Published Patent Application WO 2003/021363; and
An article titled: “Fresnel and Fourier digital holography architectures: a comparison” by Damien P., David S. Monaghan, Nitesh Pandey, Bryan M. Hennelly.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.